The invention relates to an immersion device for molten metal, the device comprising a carrier for a measuring head and a lance which is detachably connected to the carrier or can be connected to the carrier by a detachable tubular connecting element and comprising a gas path from the lance to the detachable tubular connecting element and a gas tight connection between a connecting surface of the lance and the detachable tubular connecting element. The invention further relates to a method for making steel.
An immersion device comprising a lance and a carrier is known, for example, from European patent application publication EP 0 143 498 A2. A lance of an immersion device is or can be connected to the carrier by a detachable tubular connecting element or coupling piece as known, for example, from U.S. patent application publication No. 2014/0318276 A1.
The measuring head of the carrier may comprise a sampler for taking samples from melts having a melting point higher than 600° C., in particular for metal or cryolite melts, especially iron or steel melts. The carrier may have an immersion end and a sample chamber assembly arranged on the immersion end of the carrier. The assembly may have an inlet opening and a sample cavity for the melt and can be arranged at least partially inside the carrier.
The measuring head of the carrier may comprise one or more sensors. Sensor output terminals are electrically attached to a contact end of the lance.
The lance serves for the automated machine handling or manual handling of the carrier having the measuring head. Using the lance, the carrier comprising the measuring head is immersed in the metal melt and withdrawn from the melt after obtaining the measurement and/or sample. The carrier having the measuring head is a disposable article, which is disposed of after being used once, while the lance is used multiple times.
Disposable carriers having a measuring head for obtaining measurements and metallurgical samples are described, for example, in U.S. Pat. Nos. 5,515,739 and 8,479,579 B2. These devices typically comprise a measuring head with sensors for detecting one or more of temperature, oxygen content, carbon content, bath level, and a representative sample of the liquid steel, in order to monitor the molten metal and control its processing. The measuring head is supported by the carrier protecting the internal wiring and electrical connections. The carrier is comprised of overlying layers of cardboard tubes. During immersion into molten metal, the outer circumference of cardboard deteriorates quickly but is sufficiently thick to last tens of seconds during which measurements are obtained and a metallurgical metal sample withdrawn from the bath. The measuring head is removed from the lance, the metallurgical sample retrieved and the spent probe is discarded. The DC voltage data of the sensors are automatically fed to a computer which compares the actual bath conditions with a model prediction to suggest further actions to be taken to complete the steelmaking process to the target requirements.
The accuracy of the input data is dependent upon a high quality electrical connection between the output connector of the probe and receiving contacts of the lance. Whereas, for example, a connector of a sensor is used just once and the sensor discarded after each use, the receiving contacts of the lance must be designed to withstand repeated use. When immersed into the molten steel, the cardboard carriers are heated, emitting water vapor, tar and resins present in the cardboard carriers. The water vapor transports these tars and resins which deposit upon the colder metallic portions of the electrical contact and its housing, resulting in interruption and deterioration of the electrical sensor signals and consequently in an unavailability of data or incorrect data. Each successive use of the lance deposits more and more of the tars and resins, and when these harden, they present a barrier to subsequent electrical connection, necessitating a rigorous cleaning regime that is both labor and time intensive. To combat this, a slight nitrogen purge gas is sent down the internal hollow portion of the auxiliary lance and emerges at the connector end of the lance to flush the vapor away from the contacts. Although this purge is an improvement, it does not entirely eliminate the problem. Such an internal hollow portion of the auxiliary lance is part of a gas path within the meaning of the present invention.
This condition and a solution are well described in Japanese patent application publication JP 2000-28438 A. This immersion device is equipped with an electronic circuit which digitizes the DC voltage signals and transmits these first by a single antenna wire and then by radio transmission, thus avoiding but not eliminating the problem of water, tar and resin deposition on the electrical contact members of the lance. The time and expense of cleaning is compared to the additional technical effort of the radio transmitter and as a result has found limited use.
With a sampler as described in U.S. 2014/0318276 A1, it is possible to use an inert gas purge from the lance to the sampling chamber. Reproducible gas pressure is required to obtain these rapid analysis samples, thereby necessitating an electrical and gas contact system that is free of the water, tar and resin condensates that have prevented trouble free operation of the lance measuring system.
A lance having a tubular end portion may comprise O-ring seals on the outer circumference. This tubular end portion comprising the O-ring seals has to be inserted into a detachable tubular connecting element of a coupling piece or of a carrier, in order to provide a gas tight connection between the lance and the coupling piece or the carrier. The lance and the coupling piece thus provide a gas path which may be directed to a sampling chamber.
While immersed, the purge gas flow is then implemented, as anticipated. However, once the coupling piece is disconnected, deposition of the tars and the resin on the O-rings may take place, preventing a gas tight connection between the tubular end portion of the lance and a tube of a further coupling piece.